Single Radio Voice Call Continuity (SR-VCC) has been standardized since release 8 in 3GPP TS 23.216 (version 9.3.0: Single Radio Voice Call Continuity (SRVCC); Stage 2) to provide continuity when a single radio capable User Equipment (UE) moves from E-UTRAN/HSPA (Evolved UMTS Terrestrial Radio Access Network/High Speed Packet Access) to UTRAN/GERAN (UMTS Terrestrial Radio Access Network/GSM EDGE Radio Access Network) while engaged in a voice call established over IP Multimedia Subsystem (IMS).
In SRVCC specifications up to and including release 10, only the E-UTRAN/HSPA to UTRAN/GERAN direction is addressed. How to perform subsequent handovers in the reverse direction (“handback”) was studied at the time SRVCC was first introduced (in 3GPP release 8), and a solution was proposed in 3GPP TS 23.216 (version 1.1.0: Single Radio Voice Call Continuity (SRVCC); Stage 2). But it then got subsequently removed from the specification, as it was not deemed satisfactory.
Technical report 3GPP TR 23.885 (version 0.4.0: Feasibility study of SR-VCC for UTRAN/GERAN to E-UTRAN/HSPA service continuity) has been initiated in 3GPP release 10 and is pursued in 3GPP release 11. It aims at studying how the network could handover a single radio capable UE from UTRAN/GERAN to E-UTRAN, referred to as reverse SRVCC to E-UTRAN/HSPA, or rSRVCC in the following.
All solutions currently considered for rSRVCC require that the Mobile Switching Centre (MSC) sends a message to the Serving GPRS Support Node (SGSN) at the time of the rSRVCC access transfer preparation. It is thus assumed that the source MSC knows who the source SGSN serving the UE is. However, no prior art solution existed to that problem.
Embodiments of the present invention will improve the situation. In particular, embodiments of the present invention will propose devices and methods for making it possible for a MSC to always know the address of the source SGSN.